1. Field of the Invention
The present invention relates to cable television systems, and particularly to splitter/amplifier systems for delivering diverse communication services, including voice over IP (VoIP) telephone services.
2. Description of the Related Art
Cable television operators provide a variety of diverse services to consumers. These services include high speed Internet access, video on demand, pay-per-view services, and VoIP services. Cable operators provide these services multiplexed over a single cable using such techniques as frequency division multiplexing (FDM). These services are characterized by the need to provide forward and reverse communication path. The forward path is used to transmit data to the user, while the reverse path is used to return data to the cable operator. The return data might include orders for video on demand or pay-per-view content or data transmitted by the user for destinations on the Internet.
Key components of CATV systems are drop amplifiers. These amplifiers are inserted into the cable transmission path to make up for losses in the transmission system. Signals are weakened as they pass through cables and components, such as splitters. Splitters are used to separate the services provided by the cable operator for distribution to the appropriate customer equipment for receiving the service.
Typically the return signal operates at a comparatively lower frequency than the forward path. For example, in a typical system the return signal is in a bandwidth of 5 MHz to about 40 MHz, while the forward path operates at 50-1000 MHz. Diplex filters are used to separate the combined forward and return signal into separate components for amplification using separate amplifiers. In some cases the signal level in the reverse path may be sufficiently high so that no reverse path amplifier is required. For example, set top boxes and cable modems typical provide high output levels, making the reverse path amplifier unnecessary.
Among the services provided by the cable provider, it is particularly important that the voice over IP (VoIP) service be reliable. While such services as video on demand or pay-per-view are viewed as luxury or non-essential services, VoIP is used to provide telephone communications. Telephone communication are viewed as vital services, particularly during situations involving medical emergencies or natural disasters where communications may be necessary to make essential reports, such as injuries, life threatening medical conditions, or downed power lines. The VoIP circuits may be viewed as essential services because of the need to maintain the circuits in emergency situations.
Because the amplifiers used in the systems are active components employing complex circuitry and requiring electrical power to operate, the drop amplifiers are potential failure points for VoIP services. In some situations, an emergency or disaster that requires the use of the VoIP services also results in a loss of electrical power, disabling the drop amplifiers and interrupting vital VoIP communications.
Several devices have been developed for VoIP systems. A representative device is shown in Japanese Patent No. 2004-80,483, published Mar. 11, 2004, which shows in FIG. 1 a VoIP adapter for telephone communications that switches from a telephone line network, such as a packet switched telephone network, to a VoIP network to maintain communications when a failure in the telephone line network is detected. Another representative device is shown in Japanese Patent No. 2005-5,875, published Jan. 6, 2005, which also shows in FIG. 1 a device for switching from a telephone line network, such as a packet switched telephone network, to a VoIP network to maintain communications when a failure in the power supply for the telephone line network is detected.
While the above-mentioned patent references describe circuit monitoring and switching to maintain telephone communications, neither describes maintaining VoIP communications despite failure of components in an IP network providing the VoIP infrastructure.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus, a VOIP drop amplifier solving the aforementioned problems is desired.